Found­ed in 315 B.C., the provin­cial cap­i­tal and sea port of Thes­sa­loni­ka was one of the first bases for the spread of Chris­tian­i­ty. Among its Chris­t­ian mon­u­ments are fine church­es, some built on the Greek cross plan and oth­ers on the three-nave basil­i­ca plan. Con­struct­ed over a long peri­od, from the 4th to the 15th cen­tu­ry, they con­sti­tute a diachron­ic typo­log­i­cal series, which had con­sid­er­able influ­ence in the Byzan­tine world. The mosaics of the rotun­da, St Demetrius and St David are among the great mas­ter­pieces of ear­ly Chris­t­ian art.